Remote analysis or measurement of on-road vehicle emissions is useful in determining and controlling the impact of vehicle emissions on the environment. As used here, remote analysis of on-road vehicle emissions refers to the monitoring, testing or other analysis of exhaust gas from a motor vehicle which is not physically connected to the testing apparatus and, typically, may be moving past the testing apparatus on a public roadway or the like. Studies involving remote testing of on-road vehicle emissions conducted to date having experienced significant inconsistency in test results. Two studies, for example, Stevens et al "Real World Emissions Variability as Measured by Remote Sensors" SAE Technical Paper 940582 (1984) and Stedman et al, "On-Road Remote Sensing of CO and HC Emissions in California, California Air Resources Board, Final Report AO32-093 (February, 1994), compared the output of two remote sensors measuring the same vehicles only hundreds of feet apart. These studies showed that emission measurements for the same vehicle would occasionally be significantly but unpredictably different as measured by different test devices. These vehicle have been referred to in the literature as "flippers." The flipper phenomenon has not been well understood or explained, but driver variability provides an inadequate explanation of the test differences.
A first aspect of the contribution of the present invention relates to the understanding that test result variability is explainable in large part based on the operating condition of the engine of the motor vehicle. More specifically, test result variability is now understood to be due in large measure to a vehicle being tested at a first site shortly after engine start-up when the engine and exhaust system of the vehicle have not as yet reached normal operating conditions, most particularly normal operating temperatures. The same vehicle subsequently tested at a second site, having warmed on route from the first test site to such second test site, produces substantially different emissions test results.
Accordingly, in order to effectively use remote sensing devices to analyze on-road vehicle emissions, it is now understood to be important to determine whether the vehicle being tested has reached its normal operating condition. That is, apparatus and methods for remote testing of exhaust gas emissions from an internal combustion engine of an on-road motor vehicle should include some way of remotely determining whether the engine of the tested vehicle has reached normal operating condition. Suitable methods to directly measure engine temperature of a passing vehicle would require complicated equipment and would be subject to background influences which may result in insufficient sensitivity and reliability.
It is an object of this invention to provide emissions testing apparatus and methods. It is a particular object of certain embodiments to enable remote testing of exhaust gas emissions, including means for determining whether the engine which is the source of the emissions has reached normal engine operating conditions. It is a further object to provide remote sensing methods which are suitable for use in the field with good reliability. Additional objects of the invention will be understood from the following disclosure and detailed description.